JP2020196047A - Manufacturing method of forging product - Google Patents

Abstract

To provide a manufacturing method of a forging product that uses a hot forging metal mold formed of a hot metal mold Ni group alloy having high-high temperature compression strength and excellent oxidation resistance and can restrain deterioration in a work environment and deterioration in shape in hot forging.SOLUTION: A manufacturing method of a forging product has a forging raw material heating step of heating a forging raw material having a γ' phase of 35% or higher in molar fraction to a forging raw material heating temperature of 1000°C or higher, and a hot forging step of hot-forging the forging raw material heated in the forging raw material heating step using a hot forging metal mold formed of an Ni base alloy and heated to 1000°C to the forging raw material heating temperature plus 20°C. The Ni base alloy has a composition of one or two or more kinds selected from W: 7.0-15.0%, Mo: 2.5-11.0%, Al: 5.0-7.5%, Cr: 0.5-3.0%, Ta: 0.5-7.0%, S: 0.0010% or less, a rare earth element, Y and Mg by 0-0.020%, with a residual part being Ni and an unavoidable impurity in mass % as a sum total.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for manufacturing a forged product by hot forging performed using a heated die.

In the forging of products made of heat-resistant alloys, the forged material is heated to a predetermined temperature in order to reduce deformation resistance. Since heat-resistant alloys have high strength even at high temperatures, the hot forging dies used for forging require high mechanical strength at high temperatures. Further, in hot forging, when the temperature of the hot forging die is lower than that of the forging material, the workability of the forging material is lowered due to heat removal. Therefore, for example, a product made of a difficult-to-process material such as Alloy718 or Ti alloy. Forging is performed by heating a hot forging die together with the material. Therefore, the hot forging die must have high mechanical strength at a high temperature equal to or close to the temperature at which the forging material is heated. As a die for hot forging that satisfies this requirement, a Ni-based superheat resistant alloy that can be used for hot forging with a die temperature of 1000 ° C. or higher in the atmosphere has been proposed (see, for example, Patent Documents 1 to 5).
The hot forging referred to in the present invention includes hot die forging in which the temperature of the hot forging die is brought close to the temperature of the forging material and constant temperature forging in which the temperature is the same as that of the forging material.

Japanese Unexamined Patent Publication No. 62-50429 Japanese Unexamined Patent Publication No. 60-221542 Japanese Unexamined Patent Publication No. 2016-066702 Japanese Unexamined Patent Publication No. 2016-069703 U.S. Pat. No. 4,740,354

The above-mentioned Ni-based superheat-resistant alloy is advantageous in that it has high high-temperature compression strength, but in terms of oxidation resistance, fine scales of nickel oxide scatter from the mold surface during cooling after heating in the atmosphere. Therefore, there is a risk of deterioration of the working environment and shape. The problem of oxidation of the mold surface and the accompanying scale scattering is a major problem in maximizing the effect of being able to be used in the atmosphere.
An object of the present invention is hot forging using a Ni-based alloy for hot dies, which has high high-temperature compressive strength and good oxidation resistance, and can suppress deterioration of the working environment and shape deterioration in hot forging and the like. It is to provide a method of manufacturing a forged product which hot forges a difficult-to-process forging material by using a die.

The present inventor has investigated the problems of deterioration of the working environment and shape deterioration due to oxidation of the die surface and accompanying scale scattering, and hot forging made of a composition having high high-temperature compression strength and good oxidation resistance and an alloy thereof. We have found a method for manufacturing a forged product using a die and arrived at the present invention.
That is, the present invention comprises a forging material heating step of heating a forging material having a gamma prime phase of 35% or more in terms of molar fraction to a forging material heating temperature of 1000 ° C. or higher, and 1000 forging materials heated in the forging material heating step. It has a hot forging step of hot forging using a hot forging mold made of a Ni-based alloy heated to the heating temperature of the forging material plus 20 ° C., and the Ni-based alloy is mass%. W: 7.0 to 15.0%, Mo: 2.5 to 11.0%, Al: 5.0 to 7.5%, Cr: 0.5 to 3.0%, Ta: 0.5 to 7.0%, S: 0.0010% or less, one or more selected from rare earth elements, Y and Mg total 0 to 0.020%, the balance has a composition of Ni and unavoidable impurities. This is a method for manufacturing forged products.
In the present invention, in addition to the above composition, the Ni-based alloy can further contain 0.5% or less in total of one or two selected from the elements of Zr and Hf.
Further, in the present invention, in addition to the above composition, the Ni-based alloy further comprises 3.5% or less in total of one or two selected from the elements of Ti and Nb, and the content of Ta, Ti and Nb. Can be contained within the range of 1.0 to 7.0% in total.
Further, in the present invention, the Ni-based alloy can further contain 15.0% or less of Co in addition to the above composition.
Further, in the present invention, in addition to the above composition, the Ni-based alloy may further contain one or two selected from elements having C: 0.25% or less and B: 0.05% or less. it can.
Further, in the present invention, in addition to the above composition, N: 0.0005 to 0.02% can be further contained.
Further, in the present invention, the forging material can be hot forged by heating the hot forging die in a temperature range of the forging material heating temperature minus 50 to the heating temperature plus 20 ° C.

According to the present invention, work in hot forging by applying a Ni-based alloy for hot dies having high high-temperature compressive strength and good oxidation resistance to a hot forging die using a Ni-based alloy. Environmental deterioration and shape deterioration can be suppressed.

It is a figure which showed the oxidation resistance of the example of the alloy used in this invention, and the comparative example under the test condition which simulated heating and cooling by repeated use of a mold. It is a figure which showed the Charpy impact value of the example of the alloy used in this invention and the comparative example.

Hereinafter, the Ni-based alloy for hot dies used in the present invention will be described in detail. The unit of chemical composition is mass%.
<W: 7.0-15.0%>
W dissolves in the austenite matrix as well as in the gamma prime phase (γ'phase) based on Ni ₃ Al, which is a precipitation strengthening phase, to increase the high temperature strength of the alloy. On the other hand, W has an action of lowering the oxidation resistance and an action of facilitating the precipitation of harmful phases such as TCP (Topologically Close Packed) phase. The W content in the Ni-based alloy used in the present invention is 7.0 to 15.0% from the viewpoint of increasing the high temperature strength and further suppressing the decrease in oxidation resistance and the precipitation of harmful phases. The preferred lower limit for more reliably obtaining the effect of W is 10.0%, the preferred upper limit is 12.0%, and the more preferred upper limit is 11.0%.
<Mo: 2.5 to 11.0%>
Mo dissolves in the austenite matrix and also in the gamma prime phase based on Ni ₃ Al, which is a precipitation strengthening phase, to increase the high temperature strength of the alloy. On the other hand, Mo has an action of lowering oxidation resistance. The content of Mo in the Ni-based alloy used in the present invention is 2.5 to 11.0% from the viewpoint of increasing the high-temperature strength and further suppressing the decrease in oxidation resistance. In addition, in order to suppress the precipitation of harmful phases such as TCP phase due to the addition of W and Ta, Ti, Nb described later, it is preferable to set a preferable lower limit of Mo in consideration of the W, Ta, Ti, Nb content. , The preferable lower limit for obtaining the effect of Mo more reliably is 4.0%, and the more preferable lower limit is 4.5%. The preferable upper limit of Mo is 10.5%, and the more preferable upper limit is 10.2%.

<Al: 5.0-7.5%>
Al has the effect of bonding with Ni to precipitate a gamma prime phase composed of Ni ₃ Al, increasing the high temperature strength of the alloy, forming an alumina film on the surface of the alloy, and imparting oxidation resistance to the alloy. On the other hand, if the Al content is too high, the eutectic gamma prime phase is excessively generated, which also has the effect of lowering the high temperature strength of the alloy. From the viewpoint of increasing oxidation resistance and high-temperature strength, the Al content in the Ni-based alloy used in the present invention is 5.0 to 7.5%. The preferable lower limit for obtaining the effect of Al more reliably is 5.5%, and the more preferable lower limit is 6.1%. The preferable upper limit of Al is 6.7%, and the more preferable upper limit is 6.5%.
<Cr: 0.5 to 3.0%>
Cr has the effect of promoting the formation of a continuous layer of alumina on the surface or inside of the alloy and improving the oxidation resistance of the alloy. Therefore, it is necessary to contain 0.5% or more of Cr. On the other hand, if the Cr content is too high, there is also an effect of facilitating the precipitation of harmful phases such as the TCP phase. In particular, when a large amount of elements such as W, Mo, Ta, Ti, and Nb that improve the high temperature strength of the alloy are contained, a harmful phase is likely to precipitate. From the viewpoint of suppressing the precipitation of harmful phases while maintaining the content of elements that improve oxidation resistance and high-temperature strength at a high level, the Cr content in the Ni-based alloy used in the present invention is 0. It shall be 5 to 3.0%. The preferable lower limit for obtaining the effect of Cr more reliably is 1.3%, and the preferable upper limit of Cr is 2.0%.

<Ta: 0.5-7.0%>
Ta is solid-solved in a gamma prime phase composed of Ni ₃ Al in a form of substituting Al sites to increase the high temperature strength of the alloy. Further, the adhesion and oxidation resistance of the oxide film formed on the surface of the alloy are enhanced, and the oxidation resistance of the alloy is improved. On the other hand, if the Ta content is too high, it also has an effect of facilitating the precipitation of harmful phases such as the TCP phase and an effect of excessively generating a eutectic gamma prime phase and lowering the high temperature strength of the alloy. From the viewpoint of increasing oxidation resistance and high-temperature strength and suppressing precipitation of harmful phases, the Ta content in the Ni-based alloy used in the present invention is 0.5 to 7.0%. The preferable lower limit for obtaining the effect of Ta more reliably is 2.5%, and the preferable upper limit for Ta is 6.5%. When Ta is contained together with Ti or Nb described later, the upper limit of Ta is preferably 3.5%.

<S, rare earth elements, Y and Mg>
Further, in the Ni-based alloy for hot dies used in the present invention, S (sulfur) is an oxide film formed by segregation at the interface between the oxide film formed on the alloy surface and the alloy and inhibition of their chemical bonds. Decreases the adhesion of. Therefore, while restricting the upper limit of S to 0.0010% or less (including 0%), one or more selected from rare earth elements, Y and Mg elements that form sulfide with S are used as a total. It is preferably contained in the range of 0.020% or less. For these rare earth elements, Y and Mg, excessive addition will rather reduce the toughness. Therefore, the upper limit of the total amount of rare earth elements, Y and Mg is 0.020%. In addition, S is a component which can be contained as an impurity, and it exceeds 0% and remains not a little. When the S content may be 0.0001% (1 ppm) or more, one or two or more selected from rare earth elements, Y and Mg elements should be contained in the S content or more. It is good to do. In the Ni-based alloy of the present invention, the rare earth element, Y and Mg elements may be 0%.
Among the rare earth elements, La is preferably used. In addition to the action of preventing the segregation of S, La also has the action of suppressing the diffusion of the oxide film at the grain boundaries, which will be described later, and these actions are excellent. Therefore, La is selected from the rare earth elements. It is good to do. From an economic point of view, it is preferable to use Mg. Further, since Mg can be expected to have an effect of preventing cracking during casting, it is preferable to use Mg when selecting any of rare earth elements, Y and Mg. In order to surely obtain the effect of Mg, it is preferable to contain 0.0002% or more regardless of the presence or absence of S. It is preferably 0.0005% or more, and more preferably 0.0010% or more.

<Zr and Hf>
The Ni-based alloy for hot dies used in the present invention can contain one or two selected from Zr and Hf in a total range of 0.5% or less (including 0%). Zr and Hf suppress the diffusion of metal ions and oxygen at the grain boundaries by segregation of the oxide film into the grain boundaries. This suppression of grain boundary diffusion improves the adhesion between the oxide film and the alloy by lowering the growth rate of the oxide film and changing the growth mechanism that promotes the peeling of the oxide film. That is, these elements have an action of improving the oxidation resistance of the alloy by reducing the growth rate of the oxide film and improving the adhesion of the oxide film described above. In order to surely obtain this effect, it is preferable to contain 1 or 2 selected from the elements of Zr and Hf in a total of 0.01% or more. The preferred lower limit is 0.02%, and the more preferred lower limit is 0.05%. On the other hand, if the amount of Zr or Hf added is too large, an intermetallic compound with Ni or the like is excessively generated and the toughness of the alloy is lowered. Therefore, the total of one or two selected from the elements of Zr and Hf. The upper limit is 0.5%. The preferred upper limit is 0.2%, and the more preferred upper limit is 0.15%. By the way, since Hf can be expected to have an effect of preventing cracking during casting, it is preferable to use Hf when selecting either Zr or Hf.
The rare earth element Y also has an effect of suppressing diffusion at the grain boundaries of the oxide film. However, these elements have a higher effect of lowering toughness than Zr and Hf, and the upper limit of the content is low. Therefore, as the elements contained for the purpose of this action, Zr and Hf are more suitable than the rare earth elements Y. In order to improve the oxidation resistance and toughness in a well-balanced manner, it is particularly preferable to use Hf and Mg at the same time.

<Ti and Nb>
The Ni-based alloy for hot dies used in the present invention can contain one or two selected from Ti and Nb in a total range of 3.5% or less (including 0%). Similar to Ta, Ti and Nb are solid-solved in a gamma prime phase composed of Ni ₃ Al in a form of substituting Al sites to increase the high temperature strength of the alloy. Further, since it is an element that is cheaper than Ta, it is advantageous in terms of mold cost. On the other hand, if the content of Ti and Nb is too large, as with Ta, it also has the effect of facilitating the precipitation of harmful phases such as the TCP phase and the effect of excessively generating the eutectic gamma prime phase and lowering the high temperature strength of the alloy. is there. In addition, Ti and Nb have a weaker effect of increasing high temperature strength than Ta, and unlike Ta, they do not have an effect of improving oxidation resistance.
From the above, from the viewpoint of suppressing the decrease in high-temperature intensity due to the precipitation of harmful phases and the excessive formation of eutectic gamma-prime phases, the high-temperature intensity characteristics are defined while limiting the total content of Ta, Ti, and Nb. It is desirable to replace Ta with Ti or Nb, which is advantageous in terms of mold cost, within a range in which the oxidation resistance is maintained at the same level as when only Ta is contained. In the present invention, the upper limit of the total content of Ta, Ti and Nb is 7.0%, and the upper limit of the content of one or two selected from the elements of Ti and Nb is 3.5%. To do. The preferable upper limit of the total content of Ta, Ti and Nb is 6.5%, and the preferable upper limit of the content of one or two selected from the elements of Ti and Nb is 2.7%. Further, from the viewpoint of surely obtaining the effect of increasing the high temperature strength, the lower limit of the total content of Ta, Ti and Nb is set to 1.0%, and from the viewpoint of surely obtaining the effect of reducing the mold cost, Ti , The lower limit of the content of one or two selected from the elements of Nb is preferably 0.5%. The preferable lower limit of the total content of Ta, Ti and Nb is 3.0%, and the more preferable lower limit is 4.0%. The preferable lower limit of the content of one or two selected from the elements of Ti and Nb is 1.0%.
From an economical point of view, it is particularly preferable to use only Ti, and when high temperature strength is particularly important, it is particularly preferable to use only Nb. When both mold cost and high temperature strength are important, it is particularly preferable to use Ti and Nb at the same time. Further, when N, which will be described later, is actively added, Ti-based nitrides are formed by adding Ti, and when C, which will be described later, is further added, the Ti-based nitrides become precipitate nuclei of block-like carbides. It is possible to change the form of carbides from branch-like carbides, which increase the possibility of fatigue failure, to blocks. This makes it possible to suppress fatigue fracture.

<Co>
The Ni-based alloy for hot dies used in the present invention can contain Co. Co dissolves in the austenite matrix to increase the high temperature strength of the alloy. On the other hand, if the content of Co is too large, Co is an element that is more expensive than Ni, which increases the mold cost and also has the effect of facilitating the precipitation of harmful phases such as the TCP phase. Co can be contained in the range of 15.0% or less (including 0%) from the viewpoint of increasing the high temperature strength, increasing the mold cost and suppressing the precipitation of harmful phases. The preferable lower limit for surely obtaining the effect of Co is 0.5%, and more preferably 2.5%. The preferable upper limit is 13.0%.
<C and B>
The Ni-based alloy for hot molds used in the present invention is selected from C (carbon) of 0.25% or less (including 0%) and B (boron) of 0.05% or less (including 0%). It can contain one or two elements. C and B improve the strength of the grain boundaries of the alloy, and enhance the high temperature strength and ductility. Further, C also has an effect of increasing the tensile strength by forming an MC carbide together with W, Mo, Ta, Ti, Nb, Zr, Hf and the like and precipitating at the grain boundary to increase the grain boundary strength. On the other hand, if the contents of C and B are too large, coarse carbides and borides are formed, which also has an effect of lowering the strength of the alloy. Further, C lowers the high temperature strength of the alloy due to a significant decrease in the amount of Mo solid solution due to the formation of M ₆ C carbides during high temperature holding. From the viewpoint of increasing the strength of the grain boundaries of the alloy and suppressing the formation of coarse carbides and borides, the content of C in the present invention is 0.005-0.25% and the content of B is 0.005-. It is preferably 0.05%. The preferable lower limit for surely obtaining the effect of C is 0.01%, and the preferable upper limit is 0.15%. The preferable lower limit for surely obtaining the effect of B is 0.01%, and the preferable upper limit is 0.03%.
It is particularly preferable to use only C when economic efficiency and high temperature strength are important, and it is particularly preferable to use only B when ductility is particularly important. When both high temperature strength and ductility are important, it is particularly preferable to use C and B at the same time.

<N>
In N, the Ti-based nitride formed together with Ti as described above acts as a precipitation nucleus of MC carbide having a similar crystal structure, thereby lowering the tensile strength. The carbides are finely dispersed to increase the tensile strength while having a preferable shape from the viewpoint of suppressing excessive stress concentration such as a block shape or a spherical shape. This is because the concentration of alloying elements is high due to segregation at the end of solidification, and the presence of precipitated nuclei accelerates the precipitation of carbides in the molten metal rather than the precipitation in the molten metal with a limited volume between the dendrite arms. This is because it grows round and is finely dispersed in the flow of the molten metal. In addition, by precipitating the MC carbides preferentially, has the effect of reducing the tensile strength by the formation of cracks due to breakage of itself also forms the coarse M _{6 C} carbides may become a starting point of fatigue fracture It also has the effect of suppressing. On the other hand, if the N content is too high, there is also an effect of lowering the tensile strength due to excessive generation of microporosity and the like. In addition, by refining the crystal grains, the creep strength at high temperatures is reduced. From the viewpoint of increasing the tensile strength, suppressing the formation of microporosity, and suppressing the decrease in creep strength, the N content in the present invention can be 0.0005 to 0.02%. The preferable lower limit for obtaining the effect of N more reliably is 0.0050%, and the preferable upper limit of N is 0.010%.
When the N content is C content or more, not only the strength is lowered, but also other characteristics such as fatigue strength may be lowered due to the precipitation of coarse nitride due to the excess N. Therefore, it is preferable that the upper limit of the N content is the C content. The upper limit of the preferable N content is 1/10 of C. Further, it is not necessary for N and Ti to act as precipitation nuclei of all MC carbides, and it is sufficient to act only on branched MC carbides. The lower limit of N required for this is as long as the content of N is 1/100 of C. The preferred lower limit of N is 1/50 of C. Regarding this preferable N content, the relationship between N and C is shown below by a relational expression.
C / 100 ≦ N ≦ C (C and N are mass% of each component content)

<Remaining>
Other than the above-mentioned elements in the Ni-based alloy for hot molds used in the present invention, Ni and unavoidable impurities. In the Ni-based alloy for hot molds used in the present invention, Ni is a main element constituting a gamma phase (austenite phase), and also constitutes a gamma prime phase together with Al, Ta, Ti, Nb, Mo and W. Further, P, O, Si, Mn, Fe and the like are assumed as unavoidable impurities, and P and O may be contained as long as they are 0.003% or less, respectively, and Si, Mn and Fe. May be contained as long as each is 0.03% or less. In addition to the above-mentioned impurity elements, Ca can be mentioned as an element to be particularly restricted. The addition of Ca to the composition specified in the present invention significantly reduces the Charpy impact value, and therefore the addition of Ca should be avoided. Further, the Ni-based alloy used in the present invention can also be called a Ni-based heat-resistant alloy.

<Hot forging die>
In the present invention, a hot forging die using a Ni-based alloy for hot dies having the above alloy composition can be constructed. The hot forging die of the present invention can be obtained by sintering or casting an alloy powder. Casting, which has a lower manufacturing cost than sintering alloy powder, is preferable, and in order to suppress the occurrence of cracks in the material due to stress during solidification, it is preferable to use a sand mold or a ceramic mold as the mold. At least one of the molding surface or the side surface of the hot forging die used in the present invention can be a surface having a coating layer of an antioxidant. As a result, it is possible to prevent oxidation of the mold surface due to contact between oxygen in the atmosphere at a high temperature and the base metal of the mold and accompanying scale scattering, and more reliably prevent deterioration of the working environment and shape deterioration. The above-mentioned antioxidant is preferably an inorganic material made of any one or more of nitrides, oxides and carbides. This is because a dense oxygen blocking film is formed by the coating layer of nitride, oxide or carbide to prevent oxidation of the mold base material. The coating layer may be a single layer of any one of nitrides, oxides and carbides, and may have a laminated structure of a combination of any two or more of nitrides, oxides and carbides. Further, the coating layer may be a mixture of any two or more of nitrides, oxides and carbides.
The hot forging die using the Ni-based alloy for hot dies of the present invention described above has high high temperature compression strength and good oxidation resistance, and oxygen and dies in the atmosphere at high temperature. It is possible to prevent oxidation of the mold surface due to contact with the base metal and accompanying scale scattering, and more reliably prevent deterioration of the working environment and shape deterioration.

<Manufacturing method of forged products>
A manufacturing process for manufacturing a forged product using a hot forging die made of a Ni-based alloy for a hot die used in the present invention will be described.
First, the forged material targeted by the present invention is an alloy having a composition in which the gamma prime phase is 35% or more in terms of mole fraction. Typical alloys include Udimet720Li (Udimet is a registered trademark) and TMW alloy (TMW is a registered trademark). Alloys containing a large amount of these gamma prime phases have high deformation resistance during hot working, which makes hot forging difficult. The amount of precipitation of the gamma prime phase is determined by the alloy component, and can be calculated using commercially available calculation software JMatPro (Version 9.1, a product of Center Software Ltd.). The amount of the gamma prime phase precipitated here is the mole fraction of the gamma prime phase under an equilibrium state at a temperature of 760 ° C., which is a general aging treatment temperature for products.
In order to hot forge this difficult-to-process alloy, it is preferable to heat the hot forging die to a predetermined temperature or higher, or to apply hot die forging or constant temperature forging that keeps the heat after heating. The hot forging process specified in the invention will be described.
In the present invention, as a forging material heating step, the forging material is heated to a heating temperature of 1000 ° C. or higher. The reason for heating to 1000 ° C. or higher is that the temperature is the minimum necessary for hot forging the difficult-to-process alloy. The upper limit of the heating temperature may be -20 ° C, which is the temperature at which partial melting occurs at the grain boundaries in the forged material alloy. The hot forging temperature varies depending on the alloy composition and the required characteristics of the forged product. For example, in Udimet720Li having a gamma prime phase of about 45%, the temperature is about 1100 ° C.

In order to perform the hot forging, it is preferable to apply constant temperature forging or hot die forging. The temperature of the hot forging die refers to the temperature of the surface of the molding surface on which the forging material is molded into a predetermined shape.
In order to perform constant temperature forging, it is preferable to keep the hot forging die at the same temperature as the forging material, but the hot forging die is kept at a temperature of -50 to 20 ° C forging material heating temperature. It is acceptable to heat to a range. If the temperature difference between the forging material and the hot forging die becomes excessively wide, the temperature of the forging material may drop or become too high, and the internal quality of the forging material such as the metal structure may change. Preferably, the hot forging mold is heated to a temperature range of plus or minus 20 ° C. forging material heating temperature, and more preferably to a temperature range of plus or minus 10 ° C. for forging material heating temperature. Most preferably, as described above, the hot forging mold is kept at the same temperature as the forging material. When constant temperature forging is performed, the hot forging die may be heated and held at a predetermined temperature by a heating device installed in the forging device.
Further, in order to perform hot die forging, the forging material is hot forged by heating the hot forging die to a temperature range of 1000 ° C. or higher and a forging material heating temperature minus 100 ° C. The hot die forging uses a hot forging die heated to a temperature lower than that of the constant temperature forging. In hot die forging, there is a higher risk that the internal quality of the forging material, such as the metal structure, will change due to the temperature difference between the forging material and the hot forging die, as compared to the case of constant temperature forging. In addition, surface cracks may occur due to a decrease in the temperature of the surface of the forged material. Therefore, the temperature of the hot forging die is set to a temperature range of 1000 ° C. or higher and the forging material heating temperature minus 100 ° C.
The application of constant temperature forging and hot die forging should be selected in consideration of, for example, the hot workability of the forged material, the shape of the forged product (whether it is a complicated shape, etc.), the maximum press load of the hot forging device, and the like. Good. The hot forging die using the Ni-based alloy used in the present invention has the property of being capable of constant temperature forging and hot die forging even in an atmosphere at a high temperature, and is therefore known as a difficult-to-process material. It is suitable for hot forging of heat-resistant alloys and Ti alloys. Further, as described above, the Ni-based alloy used in the present invention can be hot forged in the atmosphere at a high temperature of 1000 ° C. or higher by using a component whose Cr content is particularly adjusted.

The present invention will be described in more detail in the following examples. The ingot of the Ni-based alloy for hot dies used in the present invention shown in Table 1 was produced by vacuum melting. The unit is mass%. In addition, the following ingot No. P and O contained in 1 to 18 and 21 to 24 were 0.003% or less, respectively, and N was an impurity level of less than 0.0005%. Further, Si, Mn, and Fe are 0.03% or less, respectively. No. The 19 ingots were positively added with N and contained 0.0054% N. No. Regarding P, O, Si, Mn, and Fe of 19, the above-mentioned o. Same as 1-18. No. in Table 1 1 to 19 have the chemical composition specified in the present invention, and will be described as "examples of the present invention". In addition, No. Reference numerals 21 to 24 are Ni-based alloys for hot dies that deviate from the chemical composition of the alloy used in the present invention, and will be described as "comparative examples".

A 10 mm square cube was cut out from each of the above ingots, and the surface was polished to the equivalent of No. 1000 to prepare an oxidation resistance test piece, and the oxidation resistance was evaluated. In the oxidation resistance test, a test simulating repeated use in the atmosphere as a die for hot forging was carried out.
No. which is an example of the alloy used in the present invention. Alloy Nos. 1 to 19 and Comparative Examples. Using the test pieces of 21 to 24, the test pieces were placed on a ceramic container composed of SiO ₂ and Al ₂ O ₃ and placed in a furnace heated to 1100 ° C., and the test pieces were placed at 1100 ° C. for 3 hours. A heating test was conducted in which the ceramic was taken out of the furnace and air-cooled after being held. The heating test was repeated 10 times by re-injecting after cooling in order to evaluate the oxidation resistance against repeated use.
For each test piece, the surface area and mass of the test piece were measured before the first heating test, and after the 1st to 10th heating tests, the test piece was cooled to room temperature and then the surface scale was removed with a blower. The mass was measured. The mass change per unit surface area of the test piece after each test by subtracting the mass measured before the first test from the mass measured after each test and dividing the value by the surface area measured before the first test. Was calculated. The larger the absolute value of the mass change value, the larger the amount of scale scattering per unit area. The mass change after each number of repetitions was calculated as follows. In addition, the present invention example No. For No. 20, after the odd number of tests, only the scale was removed by the blower, and the mass was not measured. The only difference between the test methods of the test in which the measurement is performed after the odd number of tests and the test method in which the measurement is not performed is the presence or absence of the measurement, and the difference does not affect the measurement result after the even number of times.
Mass change = (mass after test-1 mass before the first test) / surface area before the first test

Table 2 shows the mass change per unit surface area of the test piece calculated after each heating test. The unit of mass change is mg / cm ² . In addition, FIG. 1 (a) shows Example No. 1 to 5 and Comparative Example No. 21 and No. The relationship between the number of heating tests and the mass change of 22 is shown in FIG. 1 (b) with an enlarged vertical axis (mass change) of FIG. 1 (a).
As shown in FIG. 1 (a), Example No. of the alloy used in the present invention. 1 to 5 are Comparative Example Nos. It can be seen that the scale formation (scattering) is suppressed and the absolute value of the mass change value is smaller than that of the alloys of 21 and 22, and the alloy has good oxidation resistance against repeated use. Among them, No. 1 in which Hf was added in addition to Cr and Ta. 3. No. 1 in which Mg was added in addition to Cr and Ta. Regarding No. 4, scale scattering is suppressed as compared with Nos. 1 and 2 to which only Cr and Ta are added, and it can be seen that the oxidation resistance to repeated use is particularly excellent.
Further, as shown in FIG. 1 (b), No. 1 in which both Hf and Mg were added. No. 5 is the above-mentioned No. 3 and No. It can be seen that the oxidation resistance against repeated use is further excellent as compared with 4.
Regarding Examples 6 to 19 of the alloys used in the present invention, as shown in Table 2, Comparative Example No. It can be seen that the scale formation (scattering) is suppressed and the absolute value of the mass change value is smaller than that of the alloys of 21 and 22, and the alloy has good oxidation resistance against repeated use.

Next, Example No. of the alloy used in the present invention in Table 1. 2 to 8 and Comparative Example No. A 10 mm × 10 mm × 55 mm U-notch test piece having an ASTM E23-compliant notch depth of 2 mm was prepared from each of the 23 and 24 ingots. Using this test piece, a Charpy impact test conforming to ASTM E23 was carried out at room temperature to determine the impact value. In this impact test, as a die for hot forging, it is tested whether the die is cracked due to thermal stress generated during heating and cooling of the die, and if it is 20 J / cm ² or more, the die is cracked. It can be said that the possibility of occurrence is sufficiently low.
Table 3 shows examples of alloys used in the present invention. 2 to 8 and Comparative Example No. The Charpy impact values of 23 and 24 at room temperature are shown. Further, FIG. 2 illustrates these Charpy impact values. As shown in FIG. 2, No. 1 of the alloy example used in the present invention. Nos. 2 to 8 are Comparative Example Nos. It can be seen that the Charpy impact value is larger than that of the alloys of 23 and 24, and the possibility that the die is cracked during hot forging is sufficiently low.
Examples of alloys used in the present invention No. 7 and 8 and Comparative Example No. From the comparison of 23 and 24, the reason why the Charpy impact value of the comparative example is low is that the rare earth element (La) and Y, which have a high effect of lowering toughness, are excessively added.

Next, Example No. of the alloy used in the present invention in Table 1. 1 to 19 and Comparative Example No. A material for collecting a test piece having a diameter of 8 mm and a height of 12 mm was cut out from each of the ingots 21 to 24, and the surface was polished to the equivalent of No. 1000 to prepare a compression test piece.
A compression test was performed using this compression test piece. The compression test temperature was set to two conditions, 1000 ° C and 1100 ° C. This is mainly for confirming the application to "hot die forging" when the test temperature is 1000 ° C, and mainly for confirming the application to "constant temperature forging" when the test temperature is 1100 ° C. Is. The test conditions were a compression test performed at test temperatures of 1000 ° C. and 1100 ° C. under conditions of a strain rate of ^10-3 / sec and a compression rate of 10%. A 0.2% compressive strength was derived from the stress-strain curve obtained by the compression test, and the high-temperature compressive strength was evaluated. This compression test tests whether the die for hot forging has sufficient compressive strength even at high temperatures, and 300 MPa or more is sufficient at a test temperature of 1100 ° C. assuming constant temperature forging. It can be said that it has strong strength. It is preferably 350 MPa or more, and more preferably 380 MPa or more. Further, at a test temperature of 1000 ° C. assuming hot die forging, it can be said that the strength is sufficient if it is 500 MPa or more. It is preferably 550 MPa or more, and more preferably 600 MPa or more.
Table 4 shows examples of alloys used in the present invention No. 1 to 19 and Comparative Example No. The 0.2% compression strength at each test temperature of the test pieces 21 to 24 is shown. From Table 4, Example No. of the alloy used in the present invention. It can be seen that the compression strength at a strain rate of 10 ^-3 / sec at 1000 ° C. of 1 is 500 MPa or more. In addition, Example No. of the alloy used in the present invention. It can be seen that the compression strength of 1 to 19 at a strain rate of 10 ^-3 / sec at 1100 ° C. is 300 MPa or more, and that any of the Ni-based alloys for hot dies used in the present invention has a high high-temperature compression strength. .. In particular, No. which does not contain Ti or Nb and has a high Ta content. No. 5, which contains Ti or Nb and has a relatively low Ta content. From the results of 9 to 11, it can be seen that even if Ta is replaced with Ti or Nb, which is advantageous in terms of mold cost within the range of the present invention, sufficient high temperature strength is maintained. In addition, No. which does not contain Co. 12 and No. No. 12 has a composition in which Co is added. 14 and No. From the result of 15, it can be seen that the high temperature strength is increased by containing Co. In addition, No. The result of 20 is 460 MPa or more, and it can be seen that it has excellent high-temperature compressive strength.

Next, Example No. of the alloy used in the present invention in Table 1. Tensile test pieces with a diameter of 12 mm and a height of about 100 mm are prepared from each of the ingots 15 to 18, and a tensile test conforming to ASTM E21 is performed at 1100 ° C. to measure the drawing value, thereby achieving "constant temperature forging". The ductility of the alloy at the operating temperature when applied was evaluated. Table 5 shows No. The drawing value in the 1100 ° C. tensile test of the test pieces of 15 to 18 is shown. From Table 5, No. 1 containing no C or B. From No.15 No. 15 having a composition in which C or B is added. It can be seen that 16 to 18 have a larger aperture value and higher ductility.

Next, using a small compression tester, an experiment was conducted to simulate the production of forged products by constant temperature forging. For the forging material, a cylindrical compression material made of a Ni-based superheat-resistant alloy, the surface of which is a polished surface equivalent to No. 1000, with a diameter of 8 mm and a height of 12 mm is used, and the die is No. 1 of the alloy used in the present invention. A mold having a diameter of 15 mm and a height of 6 mm prepared from the ingot of No. 5 was used. The flow stress of the forged material at a temperature of 1100 ° C. and a strain rate of ^10-3 / sec is about 50 MPa, and the precipitation amount of the gamma prime phase of this forged material at 760 ° C. is about 45% in mole fraction. With a mica plate having a diameter of 20 mm and a thickness of 0.2 mm laid between the forging material and the mold to prevent seizure of both, one of the dies according to Example 5 of the present invention is placed above and below the forging material. They were placed one by one and mounted on a small compression tester. Then, the forging material and the die were heated to 1100 ° C. by an induction heating device attached to the testing machine, and the forging material was compressed by 60% at a strain rate of ^10-3 / sec. Since no deformation was observed in the die after the experiment in appearance, it can be seen that this die can be used for constant temperature forging of a Ni-based superheat-resistant alloy at 1100 ° C.

From the above results, the Ni-based alloy for hot dies used in the present invention has sufficient oxidation resistance even when used for hot forging in the atmosphere and high compressive strength at high temperatures. , It can be seen that the possibility of mold cracking is sufficiently low. In particular, since the scale peeling can be remarkably reduced, deterioration of the working environment and shape deterioration can be suppressed.
The Ni-based alloy for hot dies used in the present invention described above can be processed into a predetermined shape to form a hot forging die, and a forged product can be manufactured by hot forging at a die temperature of 1000 ° C. or higher. .. It can be seen that the hot forging die made of a Ni-based alloy for hot dies used in the present invention having the above-mentioned characteristics is suitable for hot die forging and constant temperature forging in the atmosphere.

Claims (7)

A forging material heating process that heats a forging material with a gamma prime phase of 35% or more in mole fraction to a forging material heating temperature of 1000 ° C or more,
A hot forging step in which the forged material heated in the forging material heating step is hot forged using a hot forging mold made of a Ni-based alloy heated to the forging material heating temperature plus 20 ° C. Have,
The Ni-based alloy is mass%, W: 7.0 to 15.0%, Mo: 2.5 to 11.0%, Al: 5.0 to 7.5%, Cr: 0.5 to 3. 0%, Ta: 0.5 to 7.0%, S: 0.0010% or less, one or more selected from rare earth elements, Y and Mg, total 0 to 0.020%, the rest A method for producing a forged product having a composition of Ni and unavoidable impurities. The method for producing a forged product according to claim 1, wherein the Ni-based alloy further contains 0.5% or less in total of one or two selected from the elements of Zr and Hf in mass%. The Ni-based alloy further contains 3.5% or less in total of one or two selected from the elements of Ti and Nb in mass%, and the total content of Ta, Ti and Nb is 1. The method for producing a forged product according to claim 1 or 2, which is 0 to 7.0%. The method for producing a forged product according to any one of claims 1 to 3, wherein the Ni-based alloy further contains 15.0% or less of Co in mass%. The invention according to any one of claims 1 to 4, wherein the Ni-based alloy further contains one or two selected from elements having C: 0.25% or less and B: 0.05% or less in mass%. How to make forged products. The Ni-based alloy for hot dies according to any one of claims 1 to 5, further containing N: 0.0005 to 0.02% in mass%. The method according to any one of claims 1 to 6, wherein the hot forging die is heated in a temperature range of the forging material heating temperature minus 50 to the forging material heating temperature plus 20 ° C. to hot forge the forging material. How to make forged products.